subsurface to surface correlation of the tensleep
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5-2014
Subsurface to Surface Correlation of the TensleepSandstone in the West Flank of the PryorMountains in Carbon County, MontanaWilliam B. RhyneMontana Tech of the University of Montana
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Recommended CitationRhyne, William B., "Subsurface to Surface Correlation of the Tensleep Sandstone in the West Flank of the Pryor Mountains in CarbonCounty, Montana" (2014). Graduate Theses & Non-Theses. Paper 2.
SubsurfacetoSurfaceCorrelationoftheTensleepSandstoneintheWestFlankofthePryorMountainsinCarbonCounty,Montana
WilliamB.Rhyne
ANon‐thesisResearchPapersubmittedinpartialfulfillmentoftherequirementsfor:
MasterofScienceDegreeGeoscience:GeologyOption
DepartmentofGeologicalEngineeringMontanaTechoftheUniversityofMontana
Butte,Montana
May12,2014
ResearchCommittee:
Dr.LarrySmith(Chair)
Mr.JohnGetty(MontanaTech,Dept.ofPetroleumEngineering)
Dr.ChrisGammons(MontanaTech,Dept.ofGeologicalEngineering)
Dr.ChadOkrusch(MontanaTech,Dept.ofTechnicalCommunication)
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Abstract
The Pennsylvanian Tensleep Sandstone is an eolian and nearshore marine/sabka
quartz arenite unit with prominent outcrops along the western Pryor/Bighorn Mountain
front east of Red Lodge, MT. Regionally, the formation represents one of the largest
ergs in the global geologic record. High permeability makes it an important oil and gas
reservoir and aquifer in south central Montana and throughout much of Wyoming. The
Tensleep Sandstone’s high percentage of quartz content and grain roundness, due to its
eolian origin, makes it a prospective source for natural proppant sand.
Three continuous 4-inch cores were obtained during a cooperative project
between Montana Tech and industry partners. Using stratigraphic sections, cores, thin
sections, and x-ray fluorescence (XRF) analysis, the usefulness and economic feasibility
of the Tensleep Sandstone as a minable hydraulic fracture proppant was explored.
Usefulness depends on cementation, grain shape, grain size, and depth from surface of
the prospective zone. Grain shape and size were determined by thin sections, sieving,
and stereomicroscope analysis. Analysis of 20 disaggregated sand samples has shown
that as much as 30 percent of the grain sizes fall between 30-50 mesh (medium- to fine-
grained sand size) and about 45 percent of the grain sizes fall between 70–140 mesh
(very fine-grained sand to coarse silt), grain sizes appropriate for some hydraulic fracture
operations. Core descriptions and XRF data display the distribution of lithology and
cementation. Elemental (XRF) analyses help to delineate more pure quartz sands from
those with grain fractions reflecting fine-grained clastic and evaporitic inputs. The core
and nearby stratigraphic sections are used to quantify the amount of overburden and the
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amount of resource in the area. Initial results show favorable crush strength and useable
grain size and shape.
Acknowledgements
I would like to express my deep appreciation and gratitude to my advisor, Dr.
Larry Smith, for his incredible insights. He was always available to answer questions and
jump right in to show me how things were done. He’s got a true passion for geology, and
that passion rubs off on his students.
I would also like to thank Mr. John Getty for allowing a budding geologist to work on
this project and his encouragement along the way.
I owe Dr. Chris Gammons a debt of gratitude for providing guidance in the elemental
analysis realm, and Dr. Chad Okrusch for his kind words in the short time he was part of
this project.
Without Asel Sherimkulova and Ryan Winter, I could not have made it through my final
year. I owe you guys big time and don’t know if I can ever buy enough rounds to make
up for your help.
My mom and dad, Barb and Dave, have spent so much time, energy, and resources on me
and my brother, I can never thank them enough.
Finally, I am so thankful to my beautiful wife Erin; my biggest supporter.
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Contents
ABSTRACT ............................................................................................................................................. 2
ACKNOWLEDGEMENTS .......................................................................................................................... 3
LIST OF FIGURES .................................................................................................................................... 6
INTRODUCTION ..................................................................................................................................... 8
GEOLOGIC HISTORY ............................................................................................................................... 9
PROCEDURES/METHODS ..................................................................................................................... 13
1. CORE DESCRIPTION .......................................................................................................................... 14
2. CRUSH TESTING ............................................................................................................................... 14
3. SIEVE TESTS .................................................................................................................................... 14
4. XRF .............................................................................................................................................. 15
5. MICROSCOPIC ANALYSIS .................................................................................................................... 15
5.1. Petrographic .................................................................................................................... 15
5.2. Binocular .......................................................................................................................... 16
6. MODAL MINERALOGY ...................................................................................................................... 16
RESULTS .............................................................................................................................................. 17
1. STRATIGRAPHIC SECTIONS ................................................................................................................. 17
1.1. SS‐5 Stratigraphic Section ................................................................................................ 19
1.2. SS‐1 Stratigraphic Section ................................................................................................ 21
1.3. Stockman Trail Stratigraphic Section ............................................................................... 23
1.4. SS‐11 Stratigraphic Section .............................................................................................. 25
1.5. Bear Canyon Stratigraphic Section ................................................................................... 27
2. CRUSH TESTING ............................................................................................................................... 29
3. SIEVING ......................................................................................................................................... 29
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4. CORRELATION ................................................................................................................................. 30
4.1. X‐ray Fluorescence (XRF) .................................................................................................. 30
4.2. Correlation of Stratigraphic Sections ............................................................................... 48
5. MICROSCOPIC ANALYSIS ................................................................................................................... 50
5.1. Petrographic .................................................................................................................... 50
5.2. Binocular .......................................................................................................................... 58
MODAL MINERALOGY ............................................................................................................................. 60
DISCUSSION ........................................................................................................................................ 62
CONCLUSION ....................................................................................................................................... 65
REFERENCES CITED .............................................................................................................................. 66
APPENDIX A – CORE LOGS ................................................................................................................... 67
APPENDIX B – XRF DATA ...................................................................................................................... 67
APPENDIX C – PROPPANT RESEARCH DIVISION DATA ........................................................................... 67
APPENDIX D – THIN SECTION PHOTOGRAPHS ...................................................................................... 67
APPENDIX E – CORE PHOTOGRAPHS .................................................................................................... 67
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List of Figures
Figure 1 - Location map of study area in south central Montana (shown in red box). ......10
Figure 2 - General Stratigraphic section for Pennsylvanian and Mississippian Age in
Montana Modified from Vuke et al. (2007). ..........................................................11
Figure 3 - Geologic map of project area (outlined in black box). Modified from Lopez
(2000). ....................................................................................................................12
Figure 4 - Core locations and measured sections with the cross section outline ...............18
Figure 5 - SS-5 Stratigraphic section, grain size chart, and crush test chart. S1 to S10
show depth of samples subject to proppant testing and thin section analysis .......20
Figure 6 - SS-1 Stratigraphic section, grain size chart, and crush test chart. S1 to S10
show depth of samples subject to proppant testing and thin section analysis .......22
Figure 7 - Stockman Trail stratigraphic section, built using surface section descriptions
from Lopez et al. (2007). .......................................................................................24
Figure 8 - SS-11 Stratigraphic section and crush test chart. S1 to S10 show depth of
samples subject to proppant testing and thin section analysis ...............................26
Figure 9 - Bear Canyon Stratigraphic section ....................................................................28
Figure 10 - Calcium and Silicon from SS-5, showing a loose inverse relationship ..........33
Figure 11 - Calcium and Silicon from SS-1, showing a loose inverse relationship ..........34
Figure 12 - Calcium and Silicon from SS-11, showing a loose inverse relationship ........35
Figure 13 - Mg vs. Ca from SS-5 with control dolomites shown by red points ................37
Figure 14 - Ca vs. Mg from SS-1 with control dolomites shown by red points ................39
Figure 15 - Ca vs. Mg from SS-11 with control dolomites shown by red points ..............41
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Figure 16 - Ca vs. Si for SS-5 showing an inverse relationship ........................................43
Figure 17 – Ca vs. Si for SS-1 showing an inverse relationship........................................45
Figure 18 – Ca vs. Si for SS-11 showing an inverse relationship ......................................47
Figure 19 - Stratigraphic cross section through area of interest with proposed correlation
of base of upper Tensleep Sandstone .....................................................................49
Figure 20 - Sample 9 from core SS-11 of subrounded-rounded quartz grains (yellow) and
open pore space (filled by blue-dyed epoxy) .........................................................51
Figure 21 - Sample 5 from core SS-11 of angular-subangular quartz grains (yellow) and
open pore space (filled by blue-dyed epoxy) .........................................................52
Figure 22 - Sample 3 from core SS-11 of subrounded-rounded quartz grains (yellow) and
open pore space (filled by blue-dyed epoxy) with some calcareous cementation .53
Figure 23 - Sample 1 from core SS-5 of subrounded-rounded quartz grains (yellow) of
varying size ............................................................................................................55
Figure 24 - Sample 4 from SS-5 of non-calcareous cementation ......................................57
Figure 25 - Sphericity of samples from SS-1 and SS-5 .....................................................59
Figure 26 - Roundness of samples from SS-1 and SS-5 ....................................................59
Figure 27 - Modal mineralogy of Sample 2 (43’) of SS-5 from Mineral Liberation
Analysis (MLA) .....................................................................................................61
Figure 28 - Final correlation of project area with potentially useful zones identified .......64
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Introduction
The Tensleep Sandstone in Central Montana has been of interest to various
industries throughout the last century for its high percentage of quartz and ease of access
for mining. In South Central Montana (Figure 1), the Tensleep Sandstone is being
investigated as a possible source for sand-sized hydraulic fracture proppant for oil and
gas well completions. Three cores were drilled in the study area and 10 samples were
taken from each core. Initial tests were done in the Proppant Research Division in the
Petroleum Engineering Department at Montana Tech of the University of Montana. The
geologic study involved using a portable X-ray Fluorescence (XRF) machine to gather
elemental analysis of each core, thin section descriptions, core descriptions, and the
surface stratigraphic sections described by Lopez et al. (2007), to create stratigraphic
columns to establish the boundary between the informal upper and lower Tensleep
Sandstone members.
All data in this report were collected on the east flank of the Pryor Mountains of
South Central Montana, roughly 6 miles north of the Wyoming - Montana border (Figure
1).
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Geologic History
The Pennsylvanian Tensleep Sandstone is a regionally important hydrocarbon
reservoir in Montana and Wyoming. The Tensleep Sandstone is part of the Wyoming
shelf lithologic province and is the equivalent of the Quadrant Quartzite in the extreme
northwestern part of Wyoming and the Weber Sandstone in northeastern Utah (Mallory,
1973). The Tensleep Sandstone was originally described in Big Horn County, Wyoming
in 1904 by Darton.
In the study area, the Tensleep Sandstone has been informally broken into an
upper and lower section and is overlain by the Phosphoria Formation and underlain by
the Amsden Formation (Figure 2). The lower member is characterized by repeated cycles
of marine sandstone capped by calcareous sandstone beds. The upper Tensleep
Sandstone member is characterized by cycles of eolian dune sandstone capped by marine
calcareous sandstone (Lopez et al., 2007).
10
Figure 1 - Location map of study area in south central Montana (shown in red box).
100 miles
11
Figure 2 - General Stratigraphic section for Pennsylvanian and Mississippian Age in Montana Modified from Vuke et al. (2007).
12
Figure 3 - Geologic map of project area (outlined in black box). Modified from Lopez (2000).
13
Procedures/Methods
Three continuous 4-inch cores were obtained by air-rotary drilling with a water-
well drilling rig in the study area. The locations of the cores were chosen strategically to
get core of the complete Tensleep Sandstone; the first location was chosen to capture the
top of the Tensleep Sandstone (SS-1). The other two cores (SS-5, SS-11) were chosen to
capture the lower sections of the Tensleep Sandstone, to a depth of over 180’. The first
core (SS-1) was cut in ¼ SW ¼ SW ¼ SW, Section 32, T8S., R26E. The second core
(SS-5) was cut in ¼ SE ¼ NW ¼ SE, Section 31, T8S., R26E. The third core (SS-11)
was cut in ¼ NW ¼ SW ¼ SW, Section 4, T9S., R26E (Figure 4).
Lopez et al. (2007) measured two surface sections in or near the study area
through the Tensleep Sandstone. The Stockman Trail section is located near drill site SS-
5 at SW ¼ Section 32 T8S R26E and the Bear Canyon section is located east of drill site
SS-11 at SE ¼ SW ¼ Section 3 T9S R26E. Descriptive data were presented in tabular
form and are summarized here to create grain size and lithology logs to provide a better
overview of the Tensleep. The distinction between the informal upper and lower
Tensleep was especially important in understanding the geologic significance of the
contact (Lopez et al., 2007). The grain sizes described in the outcrop sections ranged
from very fine to fine sand, and lithology and sedimentary structures were recorded
(Lopez et al., 2007).
Ten samples were taken from each core at depths that appeared promising as
proppant material. Jim Gruber and Dr. Larry Smith sat on the coring rig to describe the
core as it was drilled. The core was then boxed up, labeled, and sent to Montana Tech of
the University of Montana, where further work was completed.
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1. Core description
Some core descriptions were done on site during the drilling process. Where
coring became very slow due to higher induration of rocks, rotary drilling was used with
the collection of cuttings used for description. Rock type, cementation, grain size,
reaction to dilute HCl, burrowing features, color of the rock, bedding features, and a
general description of each section was completed for each core. Core descriptions were
completed in labs at Montana Tech of The University of Montana. See Appendix A for
the original core descriptions. Based on initial core description, 10 representative samples
of sandstones were chosen for proppant and thin section sample preparation.
2. Crush testing
Crush testing was conducted in the Proppant Research Division of the Petroleum
Engineering department at Montana Tech of the University of Montana. Methods used
for crush testing follow ISO 13503-2:2006 Part 2 specifications. Samples were
disaggregated by mortar and pestle and washed in a weak acid. Samples were tested at a
pressure of 5000psi. The test was done on a subsample of the rock between the #70 and
#140 size meshes. The percentage of rock that was crushed at 5000psi was measured to
indicate bulk grain strength. Samples with an increased amount of finer-grained material
after crushing suggest lower strengths. The full crush testing dataset is available in
Appendix B.
3. Sieve Tests
Sieving was conducted in the Proppant Research Division of the Petroleum
Engineering department at Montana Tech of the University of Montana. Sieving was
15
done on the 10 samples taken from SS-1 and SS-5. Methods for sieving follow ISO
13503-2:2006 Part 2 specifications. Sieve sizes used were ASTM #16, #20, #30, #40,
#50, #60, #70, and #140. All grains smaller than the #140 mesh fell into the pan. The
full sieve dataset is available in Appendix B.
4. XRF
A hand-held Niton Prospect X-Ray Fluorescence (XRF) machine was used to
create elemental analyses of each core. The XRF machine was operated in “Test-All
Geo” mode with 80 second scans. Standard soil samples of known composition were
analyzed before and after all data were taken to check instrument calibration. An XRF
reading was taken at every foot of available core. Some footage was missing from each
core where drilling complications required coring to be suspended and the rock needed to
be drilled through. In some places the rock was too soft or unconsolidated for full core
recovery. Each foot of core was visually inspected and the XRF reading was taken at a
point that best represented the foot of core. The data were then imported into Microsoft
Excel and graphed to find possible elemental relationships that could help with
correlation of stratigraphic markers between the cores.
5. Microscopic analysis
5.1. Petrographic
At each interval subjected to crush and sieve testing, a sample was cut for making
a thin section. 30 sandstone thin sections were prepared by Texas Petrographic Service
Inc., or Quality Thin Sections, Inc. All thin sections were stained with alizarin red which
helps to distinguish dolomite from calcite. Thin sections for core SS-1 and core SS-5 had
16
cover slides permanently attached for ease of use under a microscope and to decrease
issues with air bubbles trapped under cover slide interfering with visual identification of
key attributes. The depth of where each sample was taken is designated in Appendix A
in the core logs.
A Meiji ML 2000 microscope with 4x, 10x, and 40x lenses was used. Each thin
section was inspected for mineral identification of the mineral grains and cementation
between grains. Grain shape was noted and compared to a roundness chart (Powers,
1953) for accurate identification and grain size was qualitatively analyzed.
5.2. Binocular
Analysis with a binocular microscope was done by staff in the Proppant Research
Division to get an estimate of the sphericity and roundness of the grains present in each
sample. This analysis was done after sieving, using only grains between the #70 mesh
and the #140 mesh. The full dataset is located in Appendix B.
6. Modal Mineralogy
Two samples from Sample 2 of core SS-11 (36’) were analyzed by the Center for
Advanced Mineral and Metallurgical Processing (CAMP) at Montana Tech of the
University of Montana using Mineral Liberation Analysis (MLA). MLA is done by a
scanning electron microscope equipped with energy dispersive X-ray spectrometers with
software that automates the operation of the microscope (Sylvester, 2012). MLA gives a
thorough quantitative analysis of modal mineralogy by classifying the X-ray spectra of
mineral species by comparison to a library of reference spectra.
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Results
1. Stratigraphic Sections
Stratigraphic sections were created for each core using the core descriptions
gathered by Jim Gruber and Dr. Larry Smith (Figure 5 to Figure 9). Stratigraphic
sections were also created by the author for the Stockman Trail and Bear Canyon surface
sections described by Lopez et al. (2007). All stratigraphic sections were drawn to the
same scale as the sections from Lopez et al. (2007) (Figure 4). Data of grain size,
lithology and sedimentary structures are shown on the stratigraphic sections derived from
the core and surface sections were included. Rock type, grain size and sedimentary
structures were compiled on the stratigraphic sections to look for continuous stratigraphic
attributes between the cores. The range of sand grain sizes present was very fine upper,
fine upper, fine lower, medium lower, and medium upper (Wentworth, 1922). The
stratigraphic sections are discussed from northwest to southeast.
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Figure 4 - Core locations and measured sections with the cross section outline
19
1.1. SS-5 Stratigraphic Section
The SS-5 drill site is the farthest east of all the locations. Core recovery at SS-5
started at 15’ below ground level, and was completed at 135’. There is a four foot thick
limestone at 26’, and then the core is sandstone down to 108’. Tabular crossbeds are
present between 80’ and 85’ and chert nodules are recorded between 87’ and 88’. More
tabular cross bedding occurs from 88’ to 95’. Limey sandstone and sandy limestone with
some silt layers is present from 100’ to 116’. Sandstone with no bedding features is seen
from 116’ to 129’ with two 1’ limestone layers at 123’ and 127’. The core was completed
in a clay mudstone that was 5 feet thick at Total Depth (TD) (Figure 5).
20
Figure 5 - SS-5 Stratigraphic section, grain size chart, and crush test chart. S1 to S10 show depth of samples subject to proppant testing and thin section analysis
21
1.2. SS-1 Stratigraphic Section
Core SS-1 is the second most eastern drilling location. The stratigraphic section of
core SS-1 is 150’ long; recovery began 2’below ground surface. There is a 2’ limestone
from 11 to 13 feet, and then sandstone is present until 64’. That 50’ section of sandstone
is fairly homogenous, with little change in grain size, but there is crossbedding visible
from 30’ to 55’. A prominent limestone bed is seen from 64’ to 74’. The top 4’ of this
limestone has chert nodules present, and the lower 6’ of the limestone is homogenous.
Sandstone with no bedding features is seen from 74’ to 83’. Between 83’ and 84’ is
siltstone, then sandstone to 85'. A one foot limestone layer is seen at 85’. Sandstone is
from 86’ to 89’ then the core is limestone until 90’, where it becomes sandstone from 90’
to 95’. Limestone is present from 95’ to 97’. Directly below that limestone is sandstone
that extends to 116’. A foot of limestone then a foot of sandstone is seen before a cherty
dolomite at 118’. Below the dolomite is a foot of siltstone until 121’. Sandstone extends
from 121’ to 125’, where the core becomes limestone for one foot. A thin layer of
siltstone is from 126’ to 127’. Limestone extends from 127’ to 130’. The rest of the core
to TD is sandstone, with tabular crossbeds occurring from 147’ to 150’ (Figure 6).
22
Figure 6 - SS-1 Stratigraphic section, grain size chart, and crush test chart. S1 to S10 show depth of samples subject to proppant testing and thin section analysis
23
1.3. Stockman Trail Stratigraphic Section
The Stockman Trail stratigraphic section was created using data from Lopez et al.
(2007), surface description of the Tensleep Sandstone. This stratigraphic section
catalogues the complete Tensleep Sandstone, which is 186’ thick at this location.
Sandstone constitutes the top 67’ of the stratigraphic section, with high angle trough
crossbeds seen between 25’ and 35’. From 67’ to 73’, limestone is present. Between 73’
and 85’ is a sandstone with high angle trough crossbeds. From 85’ to 89’ is a dolomitic,
cherty limestone. In the large sandstone section from 89’ to 172’, crossbedding is
abundant. Tabular cross beds are present from 93’ to 97’. At 118’, more tabular
crossbeds are seen. Trough cross beds occur again between 123’ and 125’. From 136’ to
138’, tabular crossbeds exist and trough crossbeds are seen at 150’. The sandstone at
166’ shows tabular crossbeds. A thin mudstone is present 172’ to 174’. The base of the
Tensleep Sandstone on the Stockman Trail stratigraphic section is composed of 12’ of
sandstone with climbing ripples and overlies the Amsden Formation (Figure 7).
24
Figure 7 - Stockman Trail stratigraphic section, built using surface section descriptions from Lopez et al. (2007).
25
1.4. SS-11 Stratigraphic Section
The stratigraphic section for the SS-11 core is 120’ long. Core recovery began at 12’
below ground surface. Sandstone extends from the start of the core to a depth of 43’. At
43’, a 5’ thick layer of thinly bedded limestone and sandstone was recovered. From a
depth of 48’ to 119’ the interval is sandstone. From 48’ to 53’ there are no bedding
features. From 53’ to 67’, the sandstone displays tabular crossbeds. From 67’ to 83’ no
bedding features are evident. A 3’ section with tabular crossbedding starts at 83’ and
ends at 86’. After that thick section of sandstone, another thinly bedded limestone and
sandstone layer is present from 119’ to 122’. Sandstone extends from 122’ to TD of
132’. There was no crush testing or sieve testing done for this core.
26
Figure 8 - SS-11 Stratigraphic section and crush test chart. S1 to S10 show depth of samples subject
to proppant testing and thin section analysis
27
1.5. Bear Canyon Stratigraphic Section
The Bear Canyon stratigraphic section was created using Lopez et al. (2007)
surface description of the Tensleep Sandstone. This stratigraphic section catalogues the
complete Tensleep Sandstone, which is 197’ thick at this location. The uppermost 5’ are
dolomite. A sandstone with trough cross beds is seen from 5’ to 15’. At 15 feet, another
dolomite is present, this time 5’ thick, ending at 20’. From 20’ to 70’ is a sandstone with
high angle trough crossbeds. A calcareous layer is present from 70’ to 90’. The first 18’
of this layer is dolomite, with a 2’ limestone completing the layer. The top of this thick
calcareous layer marks the base of the upper Tensleep Sandstone, according to Lopez et
al. (2007). Below the limestone layer is sandstone that extends to the base of the
stratigraphic column. From 85’ to 95’, low-angle tabular crossbedding is present, then
again from 105’ to 110’. There are no bedding features from 110’ to 132’. Low-angle
trough crossbeds occur again from 132’ to 135’. The next bedding feature, ripple cross
laminations, appears from 152’ to 155’. From 156’ to 180’, there are no bedding
features. The last bedding features seen in this section are between 178 feet and 188 feet.
The basal Tensleep Sandstone in this stratigraphic section ends with a sandstone that has
no bedding features (Figure 9).
28
Figure 9 - Bear Canyon Stratigraphic section
29
2. Crush Testing
When conducting a crush test on possible fracture proppant, less than 10% of the
rock should fracture at the given pressure. At 10% on all graphs of the crush test data is a
‘failure line’ showing where samples are unusable and where the rock is potentially
strong enough to be used as proppant. All samples for this project were tested using
5,000 psi. Crush data indicate a low crush percentage rock layer in the lower Tensleep
in all the cores that is roughly 10 feet thick. Sample 4 (58’) of SS-5 shows a favorable
crush percentage of under 10% (Figure 5). Sample 8 (111’) and Sample 9 (138’) of SS-1
have a low crush percentage as well (Figure 6). Sample 7 (110’) of SS-11 also has a low
crush percentage. All of these samples are in the lower Tensleep Sandstone.
SS-1 and SS-11 both have a thin layer of low crush percentage rock very close to
the base of the upper Tensleep Sandstone contact, but it wasn’t seen in the SS-5 core,
possibly because it was stratigraphically above where the core began. The complete
dataset for the crush test is in Appendix B.
3. Sieving
The majority of the rock samples were larger than the #140 mesh, which is the
cutoff for possible hydraulic fracture proppant. Grains smaller than #140 are generally
not used for proppant. All samples from SS-5 have over 50% of grains larger than the
#140 mesh. The lowest percentage sample was Sample 7 (90’), with only 67% of the
grains larger than #140. Where the crush test shows a low crush percentage section in the
lower Tensleep Sandstone (Sample 4, 58’), the sieve test shows 79.5% of the rock with
favorable grain size. Sample 5 (69’) of SS-5 is also below 10% crushed rock and the
30
sieve test for that same sample indicates that 90.5% of the grains are larger than #140
mesh.
SS-1 has much more variability in grain size. In the lower Tensleep Sandstone
member where the crush test indicated less than 10% crushed grains, Sample 8 (111’)
has 66.7% of the rock is larger than #140. Sample 9 (138’) of SS-1 has only 34.9%
grains larger than the #140 mesh, but this sample does have a low crush percentage as
well.
The sieve data were plotted with the stratigraphic columns. The full sieve dataset
is available in Appendix B.
4. Correlation
Correlation among cores and surface sections relies on gross lithology and
physical position; elemental make-up of the lithologies by XRF scans were done to
provide additional data. The contact between the upper and lower Tensleep Sandstone on
the Bear Canyon surface stratigraphic section was extended through the study area.
4.1. X-ray Fluorescence (XRF)
The XRF data highlights calcium and silicon as elements that show possible
correlations between all the cores. Calcium levels are high in dolomite, limestone, and
carbonate cemented sandstone. Silicon levels are high in sandstones and siltstones.
Calcium and silicon should therefore be inversely related, assuming there is not a
significant amount of calcareous cement present in the sandstone. Because the top of the
lower Tensleep Sandstone is a thick calcareous unit, the contact should show up on both
the calcium and silicon graphs.
31
Much of the core appeared homogenous during visual inspection. The portable
XRF allowed a quantitative elemental assessment of the rock that wouldn’t have been
possible without a significant amount of time spend manually analyzing thin sections and
hand samples.
A spike is expected in calcium levels whenever there is a limestone or dolomite
layer. If there is a large amount of calcareous cement in a siliceous rock, the calcium
levels should spike as well, but not as high as a calcareous rock will.
Silicon shows high levels in rocks made of quartz, and a low in limestones and
dolomites. Because the top of the basal unit of the Tensleep Sandstone is a calcareous
rock, silicon should be at a low point at that point. A large drop in silicon should
correspond to the base of the upper member of the Tensleep Sandstone.
4.1.1. Calcium and Silicon
SS-5 has a slightly different profile than SS-1. Where SS-1 had almost no
calcium in the upper Tensleep Sandstone member (shown in Figure 11), SS-5 has zones
of relatively high calcareousness throughout both the upper and lower members (Figure
10). There is one 10’ zone with almost no calcium between 73’ and 83’, which indicates
this is the only sandstone in the SS-5 location without calcareous cementation. The lower
Tensleep Sandstone does still show higher calcium levels than the upper Tensleep
Sandstone, so the marine influence is likely still occurred.
The SS-1 dataset indicates the Tensleep Sandstone has the least amount of
calcium of all the cores, especially in the upper Tensleep member. The predominant
trend of the data for SS-1 is high silicon levels, and low to zero percent calcium
throughout the majority of the core. There is a 20’ layer of rock that has mixed calcium
32
and silicon percentages, meaning there is likely calcareous cementation present. At a few
depths, the calcium and silicon values are reversed, indicating a calcite or dolomite
section.
In the lower Tensleep Sandstone, the SS-1 data suggest that there is much more
calcareousness cement in this lower section. This coincides with the idea of the lower
Tensleep Sandstone having a heavy marine influence.
SS-11 (Figure 12) has a slightly different elemental profile than the other cores.
Initial observation might indicate that a marine influence occurred in the upper Tensleep
Sandstone and not the lower because of the high calcium percentages in the upper, and
the high percentage of silicon present throughout most of the lower Tensleep Sandstone
member. The amount of silicon and calcium occurring in the upper Tensleep Sandstone
member indicate the rock present is probably sandstone with calcareous cement. These
calcareous sandstones could be marine influenced sandstones capping eolian sand
deposits.
33
Figure 10 - Calcium and Silicon from SS-5, showing a loose inverse relationship
0
5
10
15
20
25
30
35
40
45
50
55
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65
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75
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85
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105
110
115
120
0 10 20 30 40 50
depth from surface (ft)
depth from surface (ft)
wt %
SS‐5Ca and Si
Ca
Base of UpperTensleep
34
Figure 11 - Calcium and Silicon from SS-1, showing a loose inverse relationship
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
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150
155
0 10 20 30 40 50
depth from surface (ft)
depth from surface (ft)
wt %
SS‐1Ca and Si
Ca
Base of Upper Tensleep
35
Figure 12 - Calcium and Silicon from SS-11, showing a loose inverse relationship
0
5
10
15
20
25
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55
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0 5 10 15 20 25 30 35 40 45 50
depth from surface (ft)
depth from surface (ft)
wt %
SS‐11Ca and Si
Ca
Base of UppeTensleep
36
4.1.2. Ratio Relationships
Plotting the ratio of Magnesium versus Calcium and Calcium versus Silicon can
sometimes provide useful data when investigating rock types present. These ratio plots
were created for each core.
4.1.2.1. Magnesium versus Calcium
In the depositional setting of the Tensleep Sandstone, calcium is predominantly
present in limestone and magnesium is predominantly present within dolomite. The
portable XRF machine used for elemental analysis can show inaccurate levels of
elements when used on elements that are lighter atomically. One example of this is
magnesium. To correct for this possibility, two known dolomites were analyzed along
with the cores to show where pure dolomite would occur on a plot of magnesium versus
calcium. These control points are plotted with each cores data. If the data from the
cores plot near the known dolomites, it would be clear the rock is dolomitic. If the data
from the cores plot with the same trend as the control dolomite, dolomite is present in the
rock. If the percentages are low, the dolomite is likely in the cementation between the
sand grains.
4.1.2.1.1. SS-5
The majority of core SS-5’s data shows up on the same trend of the control
dolomites, suggesting a lot of dolomite is present in the core. The weight percentages of
the data points are lower than the known dolomites though, so the dolomite is likely
present between the sand grains in the rock. Four data points from core SS-5 are within
one percent of the magnesium content of the known dolomites, which suggests some rock
of the SS-5 core is dolomite.
37
Some data points have zero magnesium, and so plot on the x-axis. The points
with no magnesium do have some calcium content, but don’t have a high percentage of
calcium. Calcite cement sparsely present in sandstone could create this profile (Figure
13).
Figure 13 - Mg vs. Ca from SS-5 with control dolomites shown by red points
0
2
4
6
8
10
12
0 5 10 15 20 25 30
Mg wt %
Ca wt %
SS‐5 Dolomite
Mg vs. Ca
control dolomite
38
4.1.2.1.2. SS-1
Core SS-1 has a larger spread than the other two cores. More points lie at zero
magnesium and zero calcium, and more points lie at or near the control dolomites than
either SS-5 or SS-11. There are six points that clearly show the same percentages as
dolomite, falling very near the control dolomite points meaning there is more dolomite in
this core than the others. Many other points from this dataset also show up with no
magnesium and small amounts of calcite, indicating calcite cement is present at those
points (Figure 14).
39
Figure 14 - Ca vs. Mg from SS-1 with control dolomites shown by red points
0
2
4
6
8
10
12
0 5 10 15 20 25 30
Mg wt %
Ca wt %
SS‐1 Dolomite
Mg vs. Ca
control dolomite
40
4.1.2.1.3. SS-11
A large portion of core SS-11’s data points have very little magnesium as well as
only small amounts of calcium. The low calcium content with a zero magnesium content
likely means small amounts of calcite cementation are present, and another type of
cement is more dominant. At least three points, and as many as seven points, show the
same content of magnesium and calcium as the control dolomites (Figure 15).
41
Figure 15 - Ca vs. Mg from SS-11 with control dolomites shown by red points
0
2
4
6
8
10
12
0 5 10 15 20 25 30
Mg wt %
Ca wt %
SS‐11 Dolomite
Mg vs. Ca
control dolomite
42
4.1.2.2. Calcium versus Silicon
A plot of calcium versus silicon could potentially show the relationship of
carbonates to silicates within each core. The Tensleep Sandstone is presumably made of
silicates, but carbonates present in the cement will show up on this graph, as will all
calcareous members. All the graphs show a strong inverse linear relationship.
4.1.2.2.1. SS-5
The majority of the data points for SS-5 have less than 5% calcium and over 30%
silicon. The data with low calcium content show more variability in silica content than
the data with high calcium content. This is especially apparent for data points with less
than 15% calcium. Points greater than 15% calcium appear to have less variability in in
silica content, and the data is much more linear. The highest percentage of calcium in
this dataset, at 21% calcium, is the lowest high point of all the datasets. This suggests
there is the least amount of calcareous deposition and cementation in this core (Figure
16).
43
Figure 16 - Ca vs. Si for SS-5 showing an inverse relationship
0
5
10
15
20
25
30
0 10 20 30 40 50
Cawt %
Siwt %
SS‐5 Ca vs. Si
Ca vs. Si
44
4.1.2.2.2. SS-1
Much of SS-1’s data have less than 10% calcium. With a few exceptions, 10%
calcium is a divide, with data greater than 10% calcium showing less variability in silica
content than the data points with less than 10% calcium. This graph is the least linear of
all the cores below 10% calcium, but the data is much more linear above that. This
dataset has the highest calcium content of all the cores, with the maximum reaching
nearly 27.5% calcium. Two data points have close to zero percent silica, showing some
potential limestones or dolomites. This core is the most calcium rich of all the cores
(Figure 17).
45
Figure 17 – Ca vs. Si for SS-1 showing an inverse relationship
0
5
10
15
20
25
30
0 10 20 30 40 50
Cawt %
Siwt %
SS‐1 Ca vs. Si
Ca vs. Si
46
4.1.2.2.3. SS-11
SS-11 has the highest percentage of data at or extremely close to zero percent
calcium. Much of the data is scattered throughout the rest of the graph, and not much
data is present above 10% calcium. Ten data points are below 10% silicon on this graph,
and three of those are above 20% calcium (Figure 18).
47
Figure 18 – Ca vs. Si for SS-11 showing an inverse relationship
0
5
10
15
20
25
30
0 10 20 30 40 50
Cawt %
Siwt %
SS‐11Ca vs. Si
Ca vs. Si
48
4.2. Correlation of Stratigraphic Sections
A cross section through the project area was created in order to propose
correlations between the surface and subsurface sections. The base map for the cross
section is shown in Figure 4. The cross section is a well to well section, and includes the
core locations and the relevant surface measured sections. The complete cross section is
shown below in Figure 19.
49
Fig
ure
19
- S
trat
igra
ph
ic c
ross
sec
tion
thr
ough
are
a of
inte
rest
wit
h p
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osed
co
rrel
atio
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f b
ase
of u
pp
er T
ensl
eep
San
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one
50
5. Microscopic Analysis
The thin sections show that there is great variability in the grain size, grain shape,
porosity and cementation present in each of these cores. There are multiple grain sizes
and grain shapes in each thin section. Both calcite and dolomite are absent, as red
staining is infrequently seen in the thin sections. Every thin section has at least a small
amount of calcite and/or dolomite present, but it is appears to be secondary to siliceous or
evaporitic cements. Photographs have been taken of all thin sections and are included in
Appendix C.
5.1. Petrographic
5.1.1. Porosity
Porosity is easy to pick out in the thin sections due to the blue epoxy used
to hold the grains together on the thin section slide. All thin sections have abundant
porosity, but porosity was not quantified; thin sections with smaller grain sizes appear to
have less porosity. Sample 9 of SS-11 (Figure 20) is a good example of a relative high
porosity zone in the Tensleep Sandstone.
51
Figure 20 - Sample 9 from core SS-11 of subrounded-rounded quartz grains (yellow) and open pore space (filled by blue-dyed epoxy)
Quartz grain
Bubble in thin section
Pore space
52
Figure 21 - Sample 5 from core SS-11 of angular-subangular quartz grains (yellow) and open pore space (filled by blue-dyed epoxy)
5.1.2. Grain Shape
The Tensleep Sandstone has a range of grain shapes throughout the thin sections.
Most common is subangular to subrounded with some angular grains and some rounded
grains. Sample 5 from SS-11 (Figure 21) is an example of angular grains in the Tensleep
Sandstone. Sample 3 from SS-11 (Figure 22) shows the rounded grains present in the
Tensleep Sandstone.
53
Figure 22 - Sample 3 from core SS-11 of subrounded-rounded quartz grains (yellow) and open pore space (filled by blue-dyed epoxy) with some calcareous cementation
Pore space
Red staining of calcareous cementation
Quartz grain
54
5.1.3. Grain Size
In the thin sections made from the Tensleep Sandstone, grains more angular
appear to be smaller in size than the more rounded grains. Sample 1 from SS-5 (Figure
23) shows large grains on the bottom of the picture, and much smaller grains at the
bottom.
55
Figure 23 - Sample 1 from core SS-5 of subrounded-rounded quartz grains (yellow) of varying size
Bubble in thin section
Small quartz grains
Large quartz grain
56
5.1.4. Cementation
The thin sections do not show much calcareous cementation. There are some
faint red stains on many of the thin sections, but the majority of the cement is not stained.
Sample 3 on SS-11 (Figure 22) shows red stained cementation in pockets throughout the
thin section, but the areas of calcareousness are isolated by siliceous and possibly
evaporitic cementation.
Sample 4 of SS-5 (Figure 24) shows cementation that isn’t calcareous. There is
no red staining present anywhere in the photo.
57
Figure 24 - Sample 4 from SS-5 of non-calcareous cementation
Non-calcareous cementation
Quartz grain
58
5.2. Binocular
The average sphericity and roundness for all samples was 0.7, although there was
some variation. Sphericity ranged from 0.5 to 0.8. Roundness ranged from 0.6 to 0.8.
Sample 9 (137’) from SS-1 had the lowest sphericity of 0.5, and Sample 8 (97’) and
Sample 9 (105’) from SS-5 had the highest sphericity of 0.8 (Figure 25). SS-1 had both
the lowest and highest roundness values; Sample 9 (137’) and Sample 10 (147’) had
roundness values of 0.6. Sample 6 (61’) of SS-1 had the highest roundness value of 0.8
(Figure 26).
59
Figure 25 - Sphericity of samples from SS-1 and SS-5
Figure 26 - Roundness of samples from SS-1 and SS-5
0
20
40
60
80
100
120
140
160
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
depth (ft)
Sphericity value
Sphericity
SS‐5
SS‐1
0
20
40
60
80
100
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140
160
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
depth (ft)
Roundess value
Roundess
SS‐5
SS‐1
60
Modal Mineralogy
The results from the Mineral Liberation Analysis are shown in Figure 27. The
MLA results show no calcite in either test conducted and only a small percentage of
dolomite. Feldspar and quartz make up the vast majority of the samples tested. This
agrees with the microscopic analysis of the thin sections. Samples used for MLA are
extremely small so the absence of calcite could correspond to one of the many areas seen
in the thin sections that are not cemented by calcareous precipitates. The dolomite present
in the MLA test likely resulted from the dolomite concretions evident in the thin sections.
61
Figure 27 - Modal mineralogy of Sample 2 (43’) of SS-5 from Mineral Liberation Analysis (MLA)
62
Discussion
The base of the upper Tensleep Sandstone was picked by Lopez et al. (2007) in
his surface measured section of the Bear Canyon. The rock descriptions listed in his
paper were the basis for this project’s interpretation of where that contact is in the cores
investigated. The contact was chosen using lithology, grain size, and cementation
descriptions.
The surface sections characterizes the upper Tensleep Sandstone as eolian sand
and the lower as a marine deposit. In the Bear Canyon surface section, the upper
Tensleep Sandstone doesn’t show any calcareous cement in sandstone. Based on this,
correlating the contact was tried using the presence of calcareousness. Unfortunately, all
cores east of Bear Canyon had calcareous cement in both the upper and lower members
of the Tensleep Sandstone so basing the correlation on cementation type was fruitless.
Lopez et al. (2007), showed the contact between the upper and lower Tensleep
Sandstone is picked at the top of the highest limestone or dolomite zone thicker than 3
feet present in the Tensleep Sandstone. The surface sections also showed that high angle
trough crossbeds occurred in the upper Tensleep Sandstone member, but are not present
in the lower member. This criterion was used to correlate the base of the upper Tensleep
Sandstone in Figure 19. The depth of the contacts from each core is listed below in Table
1.
63
Core Proposed Contact Depth
SS-5 25’
SS-1 65’
Stockman Trail 67’
SS-11 43’
Table 1 - Proposed contact of the base of the upper Tensleep Sandstone
Compiling the stratigraphic sections with the XRF data and the Proppant
Research Division’s data gives a general framework for determining whether the
Tensleep Sandstone in the project area would be suitable for hydraulic fracture proppant.
Grain size, crush testing, and samples all portray the lower Tensleep Sandstone member
as coarser grained and stronger on average than the upper Tensleep. Although The lower
Tensleep is more favorable than the upper member, the potentially useful zone is only
between 10 and 50 feet thick (Figure 28). The other obstacle is the ability to disaggregate
the Tensleep Sandstone in the project area. As the thin sections and MLA results show,
not much of the cementation in any of these cores is calcite or dolomite. The most
promising footage for calcareous cementation is from 40’ to 50’ of SS-11, but the thin
sections still only spotty calcareous cement and over half of the 10’ zone is limestone.
The calcium and magnesium amounts measured by the XRF were useful in
highlighting limestones and dolomites in the cores. The XRF data also validated the core
lithology descriptions. Actual mineralogy of the cement in a sandstone can be hard to
identify in hand sample, even with dilute HCl and a hand lens.
64
Fig
ure
28
- F
inal
cor
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of
pro
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are
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ith
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iden
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65
Conclusion
The Tensleep Sandstone changes stratigraphically throughout its regional extent.
In the study area, analyzing the drilled cores and gathering portable XRF data allowed
rough characterization of the informal upper and lower units of the Tensleep Sandstone to
take place based on the surface sections measured by Lopez et al. (2007). Compiling all
the datasets on the Tensleep Sandstone in the area of interest gave insights into the
differences between the upper Tensleep Sandstone and the lower Tensleep Sandstone
members.
Creating a stratigraphic section for each core and surface sections to compare
visually was a good starting point for understanding the stratigraphic signature of the
Tensleep Sandstone in this area. Comparing the portable XRF data and the stratigraphic
sections confirmed the contact between the upper and lower Tensleep Sandstone is at the
top of a calcareous layer thicker than 3 feet.
Using the data from the Proppant Research Division, the Center for Advanced
Mineral and Metallurgical Processing, and the stratigraphic sections drawn, a better sense
of the suitability of the Tensleep Sandstone as proppant can be understood. The sieve
data shows grain sizes in the useable spectrum for proppant material. The MLA and XRF
data show areas of high silica content. The stratigraphic sections show the thickness of
possible mineable zones along with their location stratigraphically and overburden above
them. The thin sections and core descriptions show that cementation is mostly not
calcareous, which could impede use of the Tensleep Sandstone as a potential fracture
proppant.
66
References Cited
Darton, N.H., 1904, Comparison of the stratigraphy of the Black Hills, Bighorn
Mountains, and Rocky Mountain Front Range: Geological Society of America
Bulletin, v. 15, pages 379-448.
James, W.C., Sandstone Diagenesis in Mixed Siliclastic-Carbonate Sequences: Quadrant
and Tensleep Formations (Pennsylvanian), Northern Rocky Mountains: Journal of
Sedimentary Petrology, v.62, no. 5, Sept. 1992, pages 810—824.
Lopez, D.A., VanDelinder, S.W., Hendricks, M.L., Reddish-Kuzara, S., Schwartz, C.W.,
Bear Claw, D.C., 2007, Measured Sections of the Pennsylvanian Tensleep
Sandstone, Pryor and Big Horn Mountains: Montana Bureau of Mines and
Geology
Lopez, D.A., 2000, Geologic map of the Bridger 30' x 60' quadrangle, Montana: Montana
Bureau of Mines and Geology Geologic Map 58, 1 sheet, scale 1:100,000.
Mallory, W., editor, 1972, Geologic Atlas of the Rocky Mountain Region, Denver,
Colorado, Rocky Mountain Association of Geologists, pages 121-122.
Open-File Report 553, 54 pages.
Sylvester, P.J., 2012, Use of the Mineral Liberation Analyzer (MLA) for Mineralogical
Studies of Sediments and Sedimentary Rocks, St. John’s NL, Department of Earth
Sciences, Memorial University, pages 1-2.
Vuke, S.M., Porter, K.W., Lonn, J.D., and Lopez, D.A., 2007, Geologic Map of Montana:
Montana Bureau of Mines and Geology Geologic Map 62A, page 73, 2 sheets,
scale 1:500,000.
67
Wentworth, C.K., 1999, “A Scale of Grade and Class Terms for Clastic Sediments,”
Journal of Geology, pages 377-392.
Appendix A – Core Logs
Appendix B – XRF Data
Appendix C – Proppant Research Division Data
Appendix D – Thin Section Photographs
Appendix E – Core Photographs